Pulsed flashlamps are used in a variety of applications, including optical cosmetology and dermatology applications. Such lamps normally operate at a comparatively high peak voltage, current and light intensity/power. In order to achieve such high values, power supplies or drives for such lamps typically employ a storage capacitor, which is charged between flashes or pulses, in series with an inductor and some kind of switch.
Thus, referring to FIG. 1A of the drawings, there is illustrated a simplified version of a conventional flashlamp drive circuit, in which a power supply unit 100 is used to charge a relatively small capacitor 102, in this case say 500 μF. A switch 104 is provided between the capacitor 102 and the flashlamp 106. Examples of switches used in the past have included thyristors, which once turned on, generally remain on until the capacitor has fully discharged, and transistors. When the switch 104 is closed, the capacitor 102 is substantially completely discharged to the flashlamp 106, giving a drive current pulse similar to that illustrated in FIG. 1B, whereby around (say) 150J of energy (defined by the area under the curve in FIG. 1B) is delivered to the flashlamp in around 5 ms.
However, there are applications, particularly medical applications, where the shape of the optical pulses used to drive the flashlamp is important in order to achieve the desired therapeutic effect, and in particular to achieve such effect without damage to areas of the patient's body not being treated. For example, in optical dermatology, it may be desirable to rapidly heat a target chromophore to a selected temperature, and to then reduce applied energy so as to maintain the chromophore at the desired temperature. It is therefore highly desirable for the shape and duration of the optical pulses delivered to the flashlamp to be controllable.
Referring to FIG. 2A of the drawings, there is illustrated a simplified form of another known flashlamp drive circuit, in which a power supply unit 100 is used to charge a relatively large capacitor 102 (say, 0.2 F) up to, say 1500 J, and a switch 104 (embodied in this case by a transistor) is used to deliver a small portion of this total energy (say 150 J) at a time. In view of the manner of operation of this type of partial discharge system, an optical pulse can be delivered to the flashlamp 106 with a relatively uniform energy distribution, as illustrated in FIG. 2B of the drawings. Effectively, a drive system of the type illustrated in FIG. 2A of the drawings, delivers a plurality of small packets 108 of energy. Thus, in the case where 150 J of energy are delivered in a 50 ms time interval, each packet 108 will consist of 0.03 J/μs. As a result, it is possible, using such a system, to control the shape of the optical pulse delivered to the flashlamp in order to achieve the desired effect.
However, a major disadvantage of the partial discharge system described with reference to FIG. 2A of the drawings, is the size of the capacitor 102, whereas it is highly desirable in all flashlamp applications to minimise the size of the capacitor (and therefore the charge it carries) as this has the effect of minimising the size, weight and cost of the lamp drive circuitry and enhances the safety of such drive circuits by reducing shock risks.
It is an object of the present invention to provide flashlamp drive circuitry, and a corresponding method of driving a flashlamp, whereby the shape and duration of the current pulses delivered to the flashlamp is highly controllable, and the size of the storage capacitor required is significantly reduced relative to known arrangements.